Just to let you know the final outcome.
Further problems starting appearing. I couldn't tidy registry, do disk optimization or install some software updates so I turned to Norton for a general cleanup. Once that was completed one of their diagnostics indicated 0 RAM!!! So I then needed to turn to my PC manufacturer to check out my system. That resulted in the advice that I had numerous missing files and needed to do a destructive recovery. The RAM was there but not being seen by some applications!! Initially I tried the system recovery one before the destructive version. However, as I started trying to put back applications it became obvious that I did need to do the destructive recovery. I've now completed that and most of my applications are restored and updated. The last bit is reconnecting some peripherals which I've left til last. Fortunately I had a laptop where I could transfer all my user files whilst I did the restore.
Phew!!! Glad that's nearly over.
Thanks for your interest and suggestions.